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Nonlinear vibration of fluid-conveying double-walled carbon nanotubes under random material property
Get PDFIn this study, one performs the stochastic dynamic analysis of nonlinear vibration of the fluid-conveying double-walled carbon nanotubes (DWCNTs) by considering the effects of the geometric nonlinearity and the nonlinearity of van der Waals (vdW) force. Based on the Hamilton’s principle, the nonlinear governing equations of the fluid-conveying DWCNTs are derived. In order to truly describe the random material properties of the DWCNTs, the Young’s modulus of elasticity of the DWCNTs is assumed as stochastic with respect to the position. By adopting the perturbation technique, the nonlinear governing equations of the fluid-conveying can be decomposed into two sets of nonlinear differential equations involving the mean value of the displacement and the first variation of the displacement separately. Then one uses the harmonic balance method in conjunction with Galerkin’s method to solve the nonlinear differential equations successively. Some statistical dynamic response of the DWCNTs such as the mean values and standard deviations of the amplitude of the displacement are calculated. It is concluded that the mean value and standard deviation of the amplitude of the displacement increase nonlinearly with the increase of the frequencies for both cases of coupling between longitudinal displacement and transverse displacement and uncoupling between them. However, the coefficients of variation of the amplitude of the displacement remain almost constant and stay within certain range with respect to the frequency. The calculated stochastic dynamic response plays an important role in estimating the structural reliability of the DWCNTs
Feasibility and principle analyses of morphing airfoil used to control flight attitude
Get PDFMorphing airfoil technology can enable an aircraft to adapt its shape to enhance mission performance and replace the traditional flap, ailerons, elevator and rudders to optimize flight attitude control efficiency. A set of optimal airfoil shapes are obtained aimed to minimize the aerodynamic drag character by optimizing morphing configurations at different under the two-dimensional steady-flow simulation. The traditional airfoil and morphing airfoil at different are compared. It is proved that morphing wing can be used instead of a traditional wing. Couples of traditional control surface and morphing airfoil are chosen to simulate and analyze the aerodynamic difference. The flow mechanism is described on the basis of aerodynamic simulations performed by CFX. It is demonstrated why the morphing wing can provide the same with a small
Aeroelastic self-oscillations of gas seal wall
Get PDFThe channel with a moving wall is considered to describe aeroelastic oscillations induced by gas flow. One of the channel walls has two degrees of freedom and it is supported by springs and dampers. The multi-fields investigation method is based on simulation transient gas flow in the channel to calculate aerodynamic forces acting on the wall. Corresponding rigidity and damping gas flow parameters obtained from these loads are included into the wall oscillations model for the stability analysis. The models are developed for two channel types: with smooth and finned wall. Aeroelastic stability boundary is shown for both channels. An effect of structural parameters on the realization of convergent oscillation and self-oscillation modes is shown too. A paradox of system destabilization with the increasing damping is observed for a certain parameter set
Synthesis as designing of mechatronic vibrating mixed systems
Get PDFIn this paper synthesis of mechatronic vibrating mixed systems has been studied. Mechatronic structures have been built from mechanical discrete systems connected to piezoelectric actuator and external Lx Rx Cx network. By use of non-dimensional transformations mechatronic mixed structures (branched and cascade part), which must comply with the dynamical properties in the form of frequency spectrum: resonant and anti-resonant frequencies, have been received. The problem has been presented on few different examples of four degrees of freedom
An adaptive method for inertia force identification in in cantilever under moving mass
Get PDFThe present study is concerned with the adaptive method based on wavelet transform to identify the inertia force between moving mass and cantilever. The basic model of cantilever is described and a classical identification method is introduced. Then the approximate equations about the model of cantilever can be obtained by the identification method. However, the order of modal adapted in the identification methods is usually constant which may make the identification results unsatisfied. As is known, the frequency of the highest order of modal is usually higher than the frequency of the input force in forward calculation methods. Therefore, wavelet transform is applied to decompose the data of deflection. The proportion of the low frequency component is chosen as the parameter of a binary function to decide the order of modal. The calculation results show that the adaptive method adapted in this paper is efficient to improve the accuracy of the inertia force between the moving mass and cantilever, and also the relationship between the proportion of low frequency component and the order of modal is indicated
Identification of modal parameters from structural ambient responses using wavelet analysis
Get PDFRunyang suspension bridge is the longest suspension bridge in China with a main span of 1490 meters. During the construction of the bridge, a structural health monitoring system was installed, which was designed by the Southeast University. Since the bridge was open to traffic, quantities of structural ambient vibration responses have been recorded by the monitoring system. It is important to extract dynamic characteristics from these responses for structural assessment and maintenance. This paper presents the study on extraction of modal parameters from the Runyang suspension bridge structural health monitoring system records using wavelet analysis. Time-frequency domain modal identification using wavelet analysis is studied with an emphasis on the efficient approach for determination of the dilatation parameter. Then the wavelet analysis based method was adopted to identify dynamic properties including modal frequencies, mode shapes and damping ratios from the ambient vibration responses recorded by the monitoring system. Identified results were compared with those from Enhanced Frequency Domain Decomposition method and Stochastic Subspace Identification method. The differences between results are analyzed. Suggestions on future study are also given
Efficient modeling and simulations of Lamb wave propagation in thin plates by using a new spectral plate element
Get PDFA new spectral plate element is presented for modeling selectively or simultaneously the symmetric and/or anti-symmetric modes of Lamb waves propagating in thin plate structures. The Legendre polynomials and the extended form of the displacement field are used in the formulation. The diagonal mass matrix is obtained by using a simple method with less computational effort. Detailed derivations are provided. Comparisons with existing results are performed to validate the formulations as well as the written programs. Numerical calculations have been carried out for thin aluminum plates with and without damages by using the proposed spectral plate element. Comparisons reveal that the proposed spectral plate element is more effective than the spectral plate element based on Chebyshev polynomials and the 3-D spectral finite elements with the same order of Legendre polynomials as the shape functions
Wavelet transform and current signature analysis for welding machine measurement
Get PDFThis study aims to extract the stationary features from a non-stationary data using continuous wavelet transform. For this purpose a Hall effect sensor is used to obtain current measurements during the welding operation. A welding process includes several stages referred to as the initial case, transient case and operation case. In this manner, some frequency components can be determined for these cases thereby defining behavior of a particular welding machine. Regarding to the wavelet analysis results, fundamental frequency at 50 Hz is determined to be a dominant characteristic for the considered application. Moreover, side band effects are observed around the fundamental frequency. A sinusoidal waveform of 50 Hz is localized with huge amplitude values in very short time of the time-scale plane and this duration is required during the welding operation in terms of contact between the electrode and material surface
Tribological adhesion of particles in acoustic field
Get PDFThis paper investigates interaction between two particles in acoustic field. It is shown that additional oscillating movements of particles occur as a result of plain acoustic wave action. This sufficiently increases the probability of collisions between particles. Micro-displacements in the collision zone help to remove various pollutants, oxidation products and adsorbed gas molecules from surfaces of particles. Strong adhesive bonds are formed in the contact area between the particles
Analysis of damage characteristics for cracked composite structures using spectral element method
Get PDFStructural health monitoring of composites, due to their wide use, has attracted more attention. It is essential to study variations of structural dynamic characteristics caused by the damage. A cracked spectral element model is developed to study dynamics of cracked composite structures. Taking crack location as a boundary, the cracked composite beam is separated into two parts, which are connected by a spring. The spring, whose flexibility can be obtained by laws of fracture mechanics, is used to model axial-flexural coupling effect due to asymmetry of the crack. Calculated natural characteristics are in good agreement with the results of conventional finite element method. Lamb wave reflection and transmission at the crack location are also analyzed to verify the model. Formulations are derived to calculate power reflection and transmission of wave modes. The results indicate that power reflection/transmission ratio of a single mode is monotonic, which may provide some quantitative foundations for structural health monitoring